(111+121+131+141)×(121+131+141+151)−(111+121+131+141+151)× (121+131+141).

(111+121+131+141)×(121+131+141+151)−(111+121+131+141+151)× (121+131+141).

령 111+121+131+141=a,121+131+141=b,그러면 원 식=a×(b+151)-(a+151)×b=ab+151a-ab-151b=151×(a-b)=151×[(111+121+131+141)-(121+131+141)]=151×111=1561;